This invention relates to pendulous accelerometers in general and more particularly to an improved pendulous accelerometer in which the proof mass is floated in a liquid metal.
Accelerometers of the pendulous type are well known. For example, such accelerometers are disclosed in U.S. Pat. Nos. 3,680,393, 3,438,266, 3,513,711, 3,344,675 and 3,789,672. In each of these prior art devices the accelerometer comprises a proof mass which is supported to pivot about a pendulum pivot point. In general terms, means are provided to electrically sense the displacement of the proof mass from a neutral position and torquing means responsive thereto to move the proof mass back to the neutral position. In some of these prior art devices, various fluids are used in the area between the proof mass and casing to provide damping. In each case the fluid is a type of fluid which will wet the proof mass.
Although these prior art accelerometers work quite well, they do suffer from a number of disadvantages. The flexure joint which comprises the pendulum pivot point must take up the inertial forces when the proof mass experiences an acceleration along the pendulum axis or an axis normal thereto. The reaction forces occuring at the flexure cause stresses and limit the degree to which the flexure can be made angularly compliant and linearly stiff. For an ideal accelerometer, the flexture would have infinite angular compliance and infinite linear stiffness. However, such is not possible in practice and as a result these prior art devices do not attain the ideal suspension because they have high angular stiffness and a sensitivity to cross axis accelerations. Furthermore, particularly in accelerometers damped by liquids, the density and viscosity of the damping fluid is temperature sensitive and can result in errors unless compensating means are provided.
In view of these various deficiencies, the need for an improved pendulous accelerometer which more nearly approaches the ideal and is less sensitive to temperature becomes evident.